Exposure device for copying machine and the like

ABSTRACT

In an electrostatic copying machine where an original of a first size positioned on a transparent platen is illuminated by a light source and the image thereof is reflected onto a uniformly charged photosensitive layer to form a latent electrostatic image on the photosensitive layer, which is subsequently toner developed, the improvement of preventing toner deposition at a predetermined marginal area of the photosensitive layer when an original of a second size smaller than the first size is copied by the machine, the predetermined marginal area corresponding to the excess area of the first size original with respect to the second size original, the improvement comprising means for reducing the area illuminated by the light source to an area substantially the same as that of the second size original and for exposing the predetermined marginal area of the photosensitive layer in the same manner as the non-image areas of the latent electrostatic image so that when the image is toner developed, toner will deposit only on the image areas.

'United States Patent [191 Okada [4 1 July 1, 1975 EXPOSURE DEVICE FOR COPYING MACHINE AND THE LIKE [75] lnventor: Ryuzo Okada, Yamato, Japan [73] Assignee: Fuji Xerox Co., Ltd., Tokyo, Japan [22] Filed: Nov. 21, 1973 [21] App]. No.: 417,719

Primary Examiner-John M. Horan Attorney, Agent, or Firm-Gerald J. Ferguson, Jr.; Joseph J Baker [57] ABSTRACT In an electrostatic copying machine where an original of a first size positioned on a transparent platen is illuminated by a light source and the image thereof is reflected onto a uniformly charged photosensitive layer to form a latent electrostatic image on the photosensitive layer, which is subsequently toner developed, the improvement of preventing toner deposition at a predetermined marginal area of the photosensitive layer when an original of a second size smaller than the first size is copied by the machine, the predetermined marginal area corresponding to the excess area of the first size original with respect to the second size original, the improvement comprising means for reducing the area illuminated by the light source to an area substantially the same as that of the second size original and for exposing the predetermined marginal area of the photosensitive layer in the same manner as the non-image areas of the latent electrostatic image so that when the image is toner developed, toner will deposit only on the image areas.

6 Claims, 4 Drawing Figures EXPOSURE DEVICE FOR COPYING MACHINE AND THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an exposure device for a copying machine or the like, and more particularly, to an exposure device for an electrostatic copying machine employing a reflection exposure system in which an original is placed on an original holder made of transparent glass or the like (hereinafter referred to as platen), and the original is scanned by a movable light source.

2. Discussion of the Prior Art Generally, an electrostatic copying machine comprises a drum-shaped photosensitive material comprising a photoconductive material coated on a metal, a charging device for charging the photosensitive mate rial, an exposure device for imagewise discharging the surface of the charged photosensitive material, a development device for developing the charged image by use of a developer containing a resin powder (hereinafter referred to as toner") attracted by the electrostatic force of the image, a transfer device for transferring the toner image formed on the photosensitive material to an image receiver such as paper, a fixing device for fix ing the toner image on the image receiver, and a clean' ing device for cleaning the toner remaining on the photosensitive material being not transferred and so forth.

Generally, when making copies of a positive original in the above type of copying machine, and, in particular, as a result of the exposure step, charges remain on the photosensitive material in the area corresponding to the image of the original such as letters and drawings of the original and charges are extinguished or discharged in the area corresponding to the background or non-image, white portion of the original. During the subsequent development step, the charge pattern is developed into a toner image, the toner being charged to a polarity opposite of that of the charge remaining in the shape of the letters and drawings.

It sometimes happen that a copy is made without using a platen cover. On such occasions, the operator is usually in a hurry or only one copy is desired from each of a great number of originals of size A4 from a copying machine capable of taking size B4 originals.

Referring to FIG. I of the drawing, if the original 2 is smaller than the exposure range of the scanner when a copy is made with the platen cover 1 open as shown in FIG. I, the portion outside the original does not reflect light from the exposure lamp and thus this light is not projected onto the photosensitive materiai 3 and accordingly the charges 4 existing in the area on the photosensitive material corresponding to the area outside the original are not discharged. Hence, the toner also deposits onto the latter area at development station 5. This effect is quite prominent in copying machines which employ the improved development system in which half tones of photographs and solid parts of such photographic images are faithfully developed. Consequently, when the image receiver or transfer sheet is larger than the original, the marginal portion of the image receiver is blackened with toner that is, a black framed copy 6 is obtained. When the image receiver is smaller than or has the same size as the original, the toner 7 in the area corresponding to the area outside the original is not transferred to the image receiver and undersirable phenomena occur in the copying machine. That is, for example, the amount of toner consumption increases, the load on the cleaning device 8 increases, and machine contamination increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems and a primary object thereof is to provide an improved exposure device for a copying machine or the like in which the exposure area is limited to a predetermined size when an original having a smaller size than the maximum effective area of the platen is used and light outside the limited, predetermined area is reflected onto the photosensitive material or the like.

Other objects and advantages of this invention will become apparent upon reading the appended claims in conjunction with the following detailed description and the attached drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of an illustrative prior art copying machine.

FIG. 2 is a perspective view partly cut away of an illustrative embodiment of the present invention.

FIG. 3 is a cross-sectional view along the line IIIIII of FIG. 2.

FIG. 4 is a cross-sectional view for explaining the operation of the invention when an A4 size original is replaced by a B4 size original DESCRIPTION OF PREFERRED EMBODIMENT The present invention will be described in detail with reference to an illustrative embodiment thereof shown in FIGS. 2 and 4.

A transparent platen 10 is supported on a frame base (not shown) and on the platen 10 is placed an original 12 of size A4 (letter size). The maximum effective area of the platen 10 is typically the area of B4 size (legal size) and is indicated by phantom line 14. The area outside phantom line I4 is generally covered with a panel, which is omitted in the drawing for purposes of clarity. A lamp housing 20 including two parallel lamps 21 moves adjacent the lower surface of the platen 20 along a pair of guide rails 22, 22 as is known.

In accordance with the invention, a horizontally extending, reflecting plate 18 is vertically movably mounted in retaining chambers 22a, 22a formed by bent projected portions 24, 24 of the pair of guide rails 22, 22. At the center of the reflecting plate 18 is provided a cutaway portion 18a having the same width as that of the A4 size papers, and at the lower face thereof projects an engaging member 19, which removably engages a vertical wall 200 of the lamp housing 20. A solenoid I6 is provided on a framework (not shown) of the machine and a plunger 16a thereof is located in contact with the lower surface of reflecting plate 18 and upwardly biases the plate 18 in retaining chamber 220.

In ope ration, when copying an original of size A4, the plunger 16a of the solenoid I6 is retracted downward and the light reflecting plate 18 engages with the lamp housing 20 via engaging member 19 at vertical wall 200 of housing 20 as shown in FIGS. 2 and 3. The plate I8 is thus moved together with the lamp housing 20 (in the direction of an arrow b) so that it may reflect the light from lamps 2I directed outside both ends of the A4 size original 12. whereby the width of the exposure is limited to the A4 size. Therefore. the charges in the area outside the area of the original on the photosensitive material are discharged. Accordingly. no toner can deposit on the surface of the photosensitive material in such an area during the development step.

When copying an original of size B4, the plunger of solenoid l6 pushes light reflecting plate 18 up to the position shown in FIG. 4 to remove plate 18 from lamp housing 20, plate 18 being positioned in retaining chambers 220, which, as stated hereinbefore, is formed from the recessed portions of guide rails 22. Thus, only the lamp housing is moved to expose the whole area of the B4 size original.

Control of solenoid 16 may be effected by operation of appropriate selection switch buttons (not shown) provided on the exterior of the machine or it is possible to automatically retract the plunger of the solenoid l6 whenever an A4 size copying paper is placed on the copying machine, this being effected by automatic detecting means such as a photocell detector.

Although the above description has been made with particular reference to the copying of originals of B4 and A4 sizes, it will be understood that the present invention is applicable to the copying of other size originals. Further, it should be appreciated that when a copying machine is used which produces a positive copy from a negative original, light reflecting plate 18 should be replaced by a light absorbing plate--that is, a plate having a color similar to that of the background of the original.

In the present invention, excess consumption of toner is minimized to lengthen the life of the cleaning device and the speed of making one copy from one original is enhanced. The advantages of the invention are of further significance in copying machines employing a short scanning system in which the length of scanning is limited to the length of the original.

Numerous modifications of the invention will become apparent to one of ordinary skill in the art upon reading the foregoing disclosure. During such a reading, it will be evident that this invention provides a unique exposure device for accomplishing the objects and advantages hereinstated.

What is claimed is:

1. In an electrostatic copying machine where an original of a first size positioned on a transparent platen is illuminated by a light source and the image thereof is reflected onto a uniformly charged photosensitive layer to form a latent electrostatic image on the photosensitive layer, which is subsequently toner developed, the improvement of preventing toner deposition at a predetermined, marginal area of said photosensitive layer when an original of a second size smaller than said first size is copied by said machine, the predetermined marginal area corresponding to the excess area of said first size original with respect to said second size origianl, the improvement comprising a plate movably mounted with respect to said light source, said plate including an opening therein and moving means for moving said plate to: (l) a first position interposed between said light source and said transparent platen when said second size is copied, and (2) to a second position not interposed between said light source and said transparent platen when said first size original is copied, the size of the opening in said plate being such that it reduces the area illuminated by said light source to substantially that of said second size original when said plate is in said first position, the remaining light from said light source being affected by the area of said plate adjacent said opening to prevent toner deposition at said prede termined marginal area of the photosensitive layer by causing the predetermined marginal area of said photosensitive layer to be exposed in the same manner as the non-image areas of said latent electrostatic image so that when said image is toner developed. toner will deposit only on the image areas.

2. The improvement as in claim I where said light source comprises at least one elongated tube movably mounted with respect to said transparent platen for scanning an original, the opening in said plate being such that when said plate is interposed between said elongated tube and said platen, both ends of said tube are covered thereby reducing the area illuminated by said tube to approximately that of said second size original.

3. The improvement as in claim 2 where light tube is mounted within a light housing and said plate includes means for removably attaching said plate to said housing, said moving means moving said plate (I) to said first position to attach the plate to the housing so that said plate will move with the housing as the light source scans the second size original and (2) to said second position to remove the plate from the housing so that only the light source moves as it scans the first size document.

4. The improvement as in claim 1 where said first size original is B4 size (substantially legal size) and said second size original is A4 size (substantially letter size).

5. The improvement as in claim 1 where a positive copy is obtained from a positive original and said improvement comprises a light reflecting plate movably mounted with respect to said light source, said reflecting plate including an opening therein and means for moving said reflecting plate to (l) a first position interposed between said light source and said transparent platen when said second size original is copied and (2) to a second position not interposed between said light source and said transparent platen when said first size original is copied, the size of the opening in said reflecting plate being such that it reduces the area illuminated by said light source to substantially that of said second size original, the remaining light from said light source being reflected by said reflecting plate onto said photosensitive layer to discharge the charge at said predetermined marginal area and thereby prevent toner deposition thereat, said toner being charged to a polarity opposite to that of the charge on said photosensitive layer.

6. The improvement as in claim I where a positive copy is obtained from a negative original and said improvement comprises a light absorbing plate movably mounted with respect to said light source, said absorbing plate including an opening therein and means for moving said absorbing plate to (l) a first position interposed between said light source and said transparent platen when said second size original is copied and (I) to a second position not interposed between said light source and said transparent platen when said first size original is copied, the size of the opening in said reflecting plate being such that it reduces the area illumlncted by said light source to substantially that of said second size original, the remaining light from said light source being absorbed by said absorbing plate to prevent the discharge of charge at said predetermined marginal area of the photosensitive layer and thereby prevent toner deposition thereat, said toner being charged to the same polarity as of the charge on said photosensitive layer.

l l 4* ll! 

1. In an electrostatic copying machine where an original of a first size positioned on a transparent platen is illuminated by a light source and the image thereof is reflected onto a uniformly charged photosensitive layer to form a latent electrostatic image on the photosensitive layer, which is subsequently toner developed, the improvement of preventing toner deposition at a predetermined, marginal area of said photosensitive layer when an original of a second size smaller than said first size is copied by said machine, the predetermined marginal area corresponding to the excess area of said first size original with respect to said second size origianl, the improvement comprising a plate movably mounted with respect to said light source, said plate including an opening therein and moving means for moving said plate to: (1) a first position interposed between said light source and said transparent platen when said second size is copied, and (2) to a second position not interposed between said light source and said transparent platen when said first size original is copied, the size of the opening in said plate being such that it reduces the area illuminated by said light source to substantially that of said second size original when said plate is in said first position, the remaining light from said light source being affected by the area of said plate adjacent said opening to prevent toner deposition at said predetermined marginal area of the photosensitive lAyer by causing the predetermined marginal area of said photosensitive layer to be exposed in the same manner as the non-image areas of said latent electrostatic image so that when said image is toner developed, toner will deposit only on the image areas.
 2. The improvement as in claim 1 where said light source comprises at least one elongated tube movably mounted with respect to said transparent platen for scanning an original, the opening in said plate being such that when said plate is interposed between said elongated tube and said platen, both ends of said tube are covered thereby reducing the area illuminated by said tube to approximately that of said second size original.
 3. The improvement as in claim 2 where light tube is mounted within a light housing and said plate includes means for removably attaching said plate to said housing, said moving means moving said plate (1) to said first position to attach the plate to the housing so that said plate will move with the housing as the light source scans the second size original and (2) to said second position to remove the plate from the housing so that only the light source moves as it scans the first size document.
 4. The improvement as in claim 1 where said first size original is B4 size (substantially legal size) and said second size original is A4 size (substantially letter size).
 5. The improvement as in claim 1 where a positive copy is obtained from a positive original and said improvement comprises a light reflecting plate movably mounted with respect to said light source, said reflecting plate including an opening therein and means for moving said reflecting plate to (1) a first position interposed between said light source and said transparent platen when said second size original is copied and (2) to a second position not interposed between said light source and said transparent platen when said first size original is copied, the size of the opening in said reflecting plate being such that it reduces the area illuminated by said light source to substantially that of said second size original, the remaining light from said light source being reflected by said reflecting plate onto said photosensitive layer to discharge the charge at said predetermined marginal area and thereby prevent toner deposition thereat, said toner being charged to a polarity opposite to that of the charge on said photosensitive layer.
 6. The improvement as in claim 1 where a positive copy is obtained from a negative original and said improvement comprises a light absorbing plate movably mounted with respect to said light source, said absorbing plate including an opening therein and means for moving said absorbing plate to (1) a first position interposed between said light source and said transparent platen when said second size original is copied and (2) to a second position not interposed between said light source and said transparent platen when said first size original is copied, the size of the opening in said reflecting plate being such that it reduces the area illuminated by said light source to substantially that of said second size original, the remaining light from said light source being absorbed by said absorbing plate to prevent the discharge of charge at said predetermined marginal area of the photosensitive layer and thereby prevent toner deposition thereat, said toner being charged to the same polarity as of the charge on said photosensitive layer. 